This invention relates to a silica-organic polymer complex composition for the surface treatment of metals which essentially comprises silica (silicon dioxide or silicic anhydride) and organic polymer resin. More particularly, the present invention relates to a water dispersible silica-organic polymer complex composition suitable for the treatment of metals, which allows formation of a transparent coating with high hardness, good abrasion resistance and incombustibility, and eliminates the need of water washing after the treatment.
Hitherto, to give metals corrosion resistance as well as a desirable property for painting, surface treatments have widely been made by employing chromates and phospates. However, in recent years the environmental pollution caused by hexavalent chromium compound has given rise to serious social problems. For this reason, the surface treatment process in which chromate is used now necessitates a great amount of plant cost for treating waste washing water and for preventing the scatter of chromate fume. Furthermore, the dissolution of chromic acid from chemical conversion films may constitute a source of environmental pollution.
In the surface treatment process using phosphates, chemical conversion films of zinc phosphate system or iron phosphate system are generally employed. But, also in this process there occurs the problem of environmental pollution by hexavalent chromium compound because it is usually necessary for the phosphate coating film to be subjected to a sealing treatment by a chromate rinsing for the purpose of providing an adequate corrosion resistance. Further, there are other troublesome problems of treating waste water containing the reaction accelerator added to the composition of the phosphate system and metal ions, and of treating a large volume of sludge due to the dissolution of metals. The limited possibility of labour saving at the step of treatment is a further problem involved in this treatment process.